Member States shall prescribe that where tubers or plants have been designated to be contaminated under Article 5 (1) (a), testing in accordance with Article 4 (1) shall be carried out on potato stocks which are clonally related to those involved in the contamination. The testing shall be carried out on as many such tubers or plants as are needed to determine the probable primary source of infection and the extent of the probable contamination, preferably in order of degree of risk.

As a result of the testing, further designation of contamination, determination of the extent of probable contamination and demarcation of a zone shall be conducted, as appropriate, under Articles 5 (1) (a), (b) and (c) respectively.